1. Field of Invention
The present invention relates to an input device which is one of computer peripheral equipments, in particular, to a method for measuring position information of a coordinate indicator, and more particularly, to a coordinate input device and a method for measuring a distance between a coordinate indicator and a coordinate input device.
2. Description of Prior Art
A coordinate input device and a coordinate indicator are typically used as one of the computer peripheral equipments, which work by arranging a plurality of transmit coils, which are used for intermittently transmitting electromagnetic signals to a resonating circuit in the coordinate indicator, laterally in the coordinate input device. Meanwhile, a plurality of receiving coils are arranged in the coordinate input device. The receiving coils receive the electromagnetic signals transmitted by the transmit coils and sensed by the resonating circuit. The coordinate input device sends a pressure level being applied thereto and an coordinate information about the position of the coordinate indicator on the coordinate input device to a computer. The computer determines movement track of the coordinate indicator on the coordinate input device by using relevant software, for the purpose of information input such as text input or drawing.
The process for determining the coordinate information about the position of the coordinate indicator on the coordinate input device is as follows.
At one time, the plurality of coils in a set of transmit coils in the coordinate input device are conducted in sequence and transmit signals. The coordinate indicator induces the transmitted signals and transmits sensed signals back. One of the receiving coils in the set of receiving coils in the coordinate input device is then conducted and receives the sensed signals, and then the next one does. An abscissa of the coordinate indicator is thus determined in accordance with the signal intensity of the electromagnetic signals received by the receiving coils. One of the transmit coils in a set of transmit coils in the coordinate input device is conducted and transmit signals. The coordinate indicator induces the transmitted signals and transmits sensed signals back. The plurality of coils in a set of transmit coils in the coordinate input device are then conducted in sequence and receive the sensed signals. A vertical coordinate of the coordinate indicator is thus determined in accordance with the signal intensity of the electromagnetic signals received by the receiving coils.
However, the above method can not determine a distance between the coordinate indicator and the coordinate input device, though it determines the position coordinate information about the coordinate indicator in a two-dimensional plane of the coordinate input device.